Engine Misfire

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new_horizon

Member
Joined
Jan 26, 2012
Messages
33
Hi All,

I recently picked up my 2001 (Y) reg 1.6 Ford Puma and was really enjoying driving it. It felt nippy and was like a little go kart. I had a few issues with the sale, in that the gentleman told me that the timing belt had been changed, when it actually had not (I called the garage to verify).

So I had a good friend of mine change the timing belt and waterpump and the car came back. All seemed well.

However, the car seems to have developed a misfire at around 1,800 revs - second and third gear are particularly bad. If I put my foot down, the misfire is unnoticable - it is only when I am trying to drive conservatively that it happens (which is most of the time to be honest).

I've been reading through the various forums and this one seems to be the best place for the most helpful and friendly advice. I've noticed that a number of members have suggested spark plugs, HT leads, coil packs, rocker cover gasket leak and lamda sensors.

My question is - would the above symptoms not cause an Engine Management light to come on? I have had a diagnostic check run at my local Kwik Fit (where a friend of mine works and therefore just leant me the diagnostic machine) and it found no fault at all.

I really want to clear this problem and plan to dedicate some time to investigating it at the weekend - so any advice or additional checks that anyone can offer would be great.

Best wishes,

Mark
 
I just had same problem and it was a spark plug with serious damage, also didn't show up on the diagnostics! The damage was obvious so you could have a look before forking out for new ones. I also had a new coil pack as that was my first guess and that also made the car start and run a bit better in its own right.
 
As far as im aware, only a coil pack fault is likely to show up on diagnostics, or if its a 2 lambda sensor model, it will pick up a faulty lambda, but spark plugs and HT leads are fairly easy to check, you can run the engine, and pull each one off one at a time and see if the engine note changes when you pull each one off, if it doesnt, then its faulty. But if its idling ok, and it seems ok at high revs, then its more likely to to be the lambda sensor, has your exhaust gone black and sooty, more then usual? If the lambda sensor goes, the ecu thinks the car is running lean, so adds fuel to richen it up, and too much fuel causes a misfire, at low revs its more noticable because there isnt a lot of air going through the engine, but at high revs or harsh acceleration, you suddenly chuck a whole load of air into the engine, and it balances it out more, on acceleration the ecu goes into open loop, so it uses parameters set by the ecu for fuelling, but on cruising, it goes to closed loop, which means it uses information from the lambda sensor and other engine sensors to control fuelling.

Its not 100% guarenteed its your lambda, but you have the symptoms of a bad lambda in my humble opinion, also known as an 02 sensor, oxygen sensor, and hego sensor!! If you have a spark plug wrench, you can take the plugs out and have a look at them, if they are also black and sooty, and you can smell petrol when driving once the car has warmed up, then its likely to be Lambda.
 
sounds same as mine which coincidentally was just after a cambelt change. Was coil pack didnt show up on diags
 
Symptoms of a damaged coil pack generally don't dissappear when you put your foot down, the revs normally don't rise steady when accelerating, they fluctuate and drop a little, so you can feel the fault accelerating too, not just below 1800rpm!!
 
I have to agree with the Noob.

When i had a faulty coil pack the engine ran like crap even on acceleration & the idle was rubbish, but you dont mention idle in your problems.

As said above when you accelerate the car goes into open loop mode so uses the ecu configuration to fuel the car, so its not using information from the lambda. Does the car drive ok before its reached operating temperature? If so then its more likely to be lambda, because the lambda takes time to warm up, so when the car is cold, the PCM also uses open loop settings, so is not using information from the lambda, because the lambda needs to be warmed up before it gives accurate readings.

I wouldnt reccomend you go out and buy a lambda sensor straight away, get the coil pack tested too because lambdas arent cheap, but its more likely to be lambda or possibly MAF (Mass Air Flow sensor.
 
Before going to the expense of purchasing Lambda sensors and coil packs . It would be best to remove all 4 spark plugs and inspect the firing end of the plug. They should all be light brown biscuit coloured. Check the gap is 1.3mm.
On the 1.7 engine, especially after topping up with engine oil to the max mark on the dipstick ,has the tendency to seep some oil down the valve stem seals on cold start up. Once the spark plugs get fouled up they will cause the problem you describe.

If they are fouled , you can clean the plugs up with carb cleaner or replace the plugs with NGK Platinum plugs and gap to 1.3mm.

There are other problems that can cause the same problems, however this is the cheapest and most likely to try first.

the lambda sensor will show a fault on a scan tool if it's faulty.

They have an inbuilt heater element to warm up the sensor at idle , as it needs to be within a specified temperature range The sensors only work effectively when heated to approximately 316 °C (600 °F).
 
no i must admit i didnt read the bit about it being ok when foot down, mine was throughout the rev range.
 
HT problems (plugs, leads etc) are usualy most noticable at lower revs and full throttle opening, ie high load, so problem may be else where. I have an occasional high load low revs misfire and am suspecting plugs, after checking them today, but may also change the leads as they may be the origanals and therefor 107k old.
 
Hi All,

I just wanted to update this post as I know that many people don't once they have found a solution.

I checked all of the spark plugs for oil and age - they didn't look old and there was no sign of oil - so discounted the rocker cover gasket. I borrowed some HT leads from a Focus and swapped them over - hey presto, the problem seemed to stop when I took it for a test run.

I've just ordered a new set of HT leads and will fit this week - so will keep you all posted.

Thanks very much for your help so far! Hopefully my car will be running like a 45k mile Puma by the end of the week!
 
Hi again,

So I fitted the new HT leads and there seemed to be a difference initially, but now...same problem. Misfiring at low revs - basically if I try to drive the car in 5th gear at 30 mph, it's misfiring. Generally between 1200-1800 revs.

So...thoughts are welcome on the next port of call - Lambdar sensors? The car has two as far as I can see...

Does anyone think that it could be due to the timing? I don't recall the problem existing before the belt was changed - could it be a tooth out? If so, would this throw a warning light up?

I'm not flush with cash so just want to check all of my options before I replace lots of parts.

Any thoughts are welcome,

Thanks!

Mark
 
So I've not replaced the spark plugs, HT leads and borrowed a donor coil pack - still no difference! :cry:

Could it be fuel filter or throttle body related? Any help would be really good!

Thanks
 
Hey Tom,

I'm based in Camberley, Surrey - thanks for the offer - where abouts are you?

I should mention that there are no dash lights on and I borrow a Bosch scanner from my local Kwik Fit and it did not find any faults at all...

Thanks
 
Ahhh I'm just north of London, outside Stevenage. My lil Ka was missing for ages before it brought the light on and it turned out to be an injector that had gone down. I put a new set of plugs and a coil pack on it and it was still the same. It it were a lambda sensor it should bring the light on instantly, though having said that it should have done the same with my injector. What injectors are you running, ie what do they look like, I may have some in the garage that I could send to you to try?
 
As i said further up the page, your symptoms dont sound like the usual problems of coil pack or HT leads, but at least you can rule them out now. Do you have a spark plug wrench? If so, take your spark plugs out, and check if they are black and sooty, and the exhaust tail pipe looks more black and sooty then usual, then its more likely to be an over fuelling issue. Try resetting your ECU by disconecting the battery for 15 mins. Then drive it from cold, and see if it drives ok for the 1st 5-10 mins. That will reset the ecu, and when the lambda is cold, the ecu wont use the signal from it, so it should use factory settings until itw warmed up. If that works, then its likely to be the lambda.

Not sure if this will work, but its worth a shot. The 1.7 uses the signal from the water temp sensor to know when the engine is hot enough to use the signal from the lambda. In theory, if you reset the ecu, and unplug the water temp sensor, it should stop the ecu from using the lambda sensor to fuel the engine, and use the factory settings. It will run slightly rich, and use more fuel then it should, but then it will use less fuel then you are now if the lambda is nackard.

Just a few thoughts that might help.
 
Hi All,

I'm not sure what injectors I have - I will try and have a look at them at the weeked (it's always too dark when I finish work lately). Thanks for the offer though! Were your symptoms similar to mine then?

PumaNoob - do you know if the 1.6 model has one or two sensors? I have checked the exhaust and if anything it is remarkably clean - not sign of soot at all - the plugs were a sort of browny colour when I replaced them so I'm not sure if it is a lambdar sensor issue (based on what you have said). I will try resetting the ECU - I assume that I will lose the radio code if I do that?

Best wishes,

Mark
 
If you loose the radio code, pm me for what to do, I can sort that out for you. I don't know a lot about the 1.6, so I cant say if there are 1 or 2 water temp sensors, but either way, there will only be 1 going to the ECU, which will be the 2 pin sensor going into the water outlet housing. I can post up a pic of the 1.7 water temp sensor, it's pretty much the same as the 1.7, so might be in the same place. When you checked the plugs last, was the engine misfiring? Just thought I'd check because if you checked them when the car was running fine, they wouldn't show signs of over fuelling. That said, if you checked them and they were brown while the car was running badly, then it's not likely to be over fuelling. The tail pipe being sooty isn't a definite because the carbon can get clogged up in the cat, so doesn't make it to the tail pipe.

If the spark plugs had little light colour speckles on, then its running lean, so that perticar cylinder could have an injector issue as mentioned above. But 1 or more injectors going down isn't likely to cause your symptoms. A bad injector is more likely to fail when the engine is under load, because its under more fuel pressure from the fuel pump. It is possible though.

All the simpler issues seem to have been covered, so the next think would be to get a compression test done. If you have too low compression on 1 or more cylinders, that can cause a misfire.
 

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